Adaptive beam-steering methods to maximize wireless link budget and reduce delay-spread using multiple transmit and receive antennas

ABSTRACT

A method and apparatus for adaptive beam-steering are disclosed. In one embodiment, the method comprises performing adaptive beam steering using multiple transmit and receive antennas, including iteratively performing a pair of training sequences, wherein the pair of training sequences includes estimating a transmitter antenna-array weight vector and a receiver antenna-array weight vector.

This is a divisional of application Ser. No. 11/706,711, filed on Feb.13, 2007 now U.S. Pat. No. 7,710,319, entitled “Adaptive Beam-SteeringMethods to Maximize Wireless Link Budget and Reduce Delay-Spread UsingMultiple Transmit and Receive Antennas,” assigned to the corporateassignee of the present invention and incorporated herein by reference.

This application claims the benefit of and incorporates by referenceU.S. Provisional Application No. 60/773,508, entitled “AdaptiveBeam-Steering Methods to Maximize Wireless Link Budget and ReduceDelay-Spread Using Multiple Transmit and Receive Antennas,” filed Feb.14, 2006.

BACKGROUND OF THE INVENTION

In most wireless communication systems, the air link consists of thepropagation channel between one transmit antenna and one receiveantenna. However, it has been established that using multiple antennasat the transmitter and the receiver can significantly increase the linkbudget and consequently, link capacity. The drawback of this approach isthat the complexity of the system can also increase dramatically.Systems with multiple transmit and receive antennas are referred to aswireless MIMO (Multi-Input Multi-Output) systems.

For MIMO systems, the increase in link budget or link capacity isachieved via one of the following approaches: increasing diversity,multiplexing, and beam-forming. When using an approach that increasesdiversity, similar replicas of the signal are transmitted and receivedby multiple antennas. These multiple transmissions are either separated(made uncorrelated) in time by using distinct delays, or in frequency byusing distinct frequency offsets, or in code-space by using specificpermutations and/or coding. Multiple receptions are combined using theoptimal Maximal-Ratio-Combining (MRC) receiver. This approach does notrequire knowledge of the channel transfer function at the transmitterside. In some approaches, however, it requires significant portions ofthe transmit and receive data-path (analog and digital front-end) to bereplicated for each antenna.

Most of the current MIMO systems follow the first (diversity) approachmentioned above. The link budget produced by this approach is roughly Ntimes less than that resulting from beam-forming, where N is the numberof antennas. Also, in most cases, the existing implementations requirecomplex systems where entire analog and digital front-end portions ofdata-path are replicated per antenna. In a multiplexing scheme, accurateknowledge of the channel transfer function is used to shape the overalltransmit-to-receive transfer function into separate (orthogonal)transmission links, over which data is multiplexed by using propercoding and power distribution based on the water-filling principle (morepower and data over stronger links). As mentioned, this approachrequires some knowledge of the channel transfer function at thetransmitter side. It also requires significant portions of the transmitand receive data-path (analog and digital) to be replicated for eachantenna. However, if optimally-designed, it can provide maximumcapacity.

There are implementations based on the multiplexing approach, but theircomplexity is rather prohibitive for consumer and mobile wirelessapplications, unless the dimension of the MIMO system, i.e. the numberof antennas, are limited, which in turn limits the maximum achievablelink budget increase. In a beam-forming approach, accurate knowledge ofthe channel transfer function is used to focus the transmission over thestrongest subspace, referred to as eigenvector, of the overalltransmit-to-receive channel. The signal is then transmitted over thatsubspace. This is accomplished by proper adjustment of the signal phase,and possibly gain, for each transmit and receive antenna separately.This scheme clearly requires some knowledge of the channel transferfunction at the transmitter side. However, it can ideally be implementedwith replicating only a subset of the analog data-path, and thereforecan require much simpler implementation, and/or allow a larger number ofantennas to be used. It also provides better link budget than theincreasing diversity approach described above and for channels that arehighly correlated can approach the capacity of the multiplexing methoddescribed above. This method requires the transmission bandwidth to be asmall fraction of the carrier frequency. Note that multiplexing can beaccomplished via parallel beam-forming along the various eigenvectors ofthe transmit-to-receive channel.

Beam-forming implementations can mostly be found in radar applications,where firstly the transmitter and receiver units are the same, andsecondly the objective of beam-forming is completely different from linkbudget or link capacity maximization. Other beam-forming proposals usedirect Singular-Value Decomposition techniques that result in verycomplex implementations that are not suitable for consumer and mobilewireless applications, and consequently put limits on the dimension ofthe MIMO system, i.e. the number of antennas, and hence, the maximumachievable link budget increase.

SUMMARY OF THE INVENTION

A method and apparatus for adaptive beam-steering are disclosed. In oneembodiment, the method comprises performing adaptive beam steering usingmultiple transmit and receive antennas, including iteratively performinga pair of training sequences, wherein the pair of training sequencesincludes estimating a transmitter antenna-array weight vector and areceiver antenna-array weight vector.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the invention, which, however, should not be taken tolimit the invention to the specific embodiments, but are for explanationand understanding only.

FIG. 1 is a block diagram of one embodiment of a communication system

FIG. 2 is a block diagram of one embodiment of an integrated device.

FIGS. 3A and 3B illustrate the various Beam-Search steps.

FIG. 4 illustrates one embodiment of a beam-steering state machine.

FIG. 5 illustrates stages of one embodiment of the beam search process.

FIG. 6 illustrates a particular beam-forming that resulted from the beamsearch process of FIG. 5.

FIG. 7 illustrates one embodiment of a beam search and tracking diagramat the source/transmitter and destination/receiver respectively.

FIG. 8 is an example of a Hadamard matrix.

FIG. 9 is a flow diagram of one embodiment of the beam-tracking process.

FIG. 10 illustrates an alternative embodiment of a beam-search process.

FIG. 11 illustrates the notion of a clustered propagation channel.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

An efficient and adaptive technique to perform beam-forming fortime-varying propagation channels with reduced, and potentially minimum,complexity and increased, and potentially maximum, gain. As opposed toexisting solutions, beam-forming is performed without directlyperforming Singular-Value Decomposition (SVD), which is very complex toimplement. Instead the optimum channel eigenvector, or subspace, isobtained via an adaptive iterative scheme.

A secondary effect of beam-forming is that the resulting beam-formedchannel would normally have shorter delay-spread, meaning that theInter-Symbol Interference (ISI) window will also be shorter.

In the following description, numerous details are set forth to providea more thorough explanation of the present invention. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without these specific details. In other instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention.

Some portions of the detailed descriptions that follow are presented interms of algorithms and symbolic representations of operations on databits within a computer memory, or equivalent electronic computingdevice. These algorithmic descriptions and representations are the meansused by those skilled in the data processing arts to most effectivelyconvey the substance of their work to others skilled in the art. Analgorithm is here, and generally, conceived to be a self-consistentsequence of steps leading to a desired result. The steps are thoserequiring physical manipulations of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. It has proven convenient at times,principally for reasons of common usage, to refer to these signals asbits, values, elements, symbols, characters, terms, numbers, or thelike.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes by using digital components, or it may comprise ageneral purpose computer selectively activated or reconfigured by acomputer program stored in the computer. Such a computer program may bestored in a computer readable storage medium, such as, but is notlimited to, any type of disk including floppy disks, optical disks,CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), randomaccess memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, orany type of media suitable for storing electronic instructions, and eachcoupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming, or digital design, languages may be used toimplement the teachings of the invention as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; electrical, optical,acoustical or other form of propagated signals (e.g., carrier waves,infrared signals, digital signals, etc.); etc.

An Example of a Communication System

FIG. 1 is a block diagram of one embodiment of a communication system.Referring to FIG. 1, the system comprises media receiver 100, a mediareceiver interface 102, a transmitting device 140, a receiving device141, a media player interface 113, a media player 114 and a display 115.

Media receiver 100 receives content from a source (not shown). In oneembodiment, media receiver 100 comprises a set top box. The content maycomprise baseband digital video, such as, for example, but not limitedto, content adhering to the HDMI or DVI standards. In such a case, mediareceiver 100 may include a transmitter (e.g., an HDMI transmitter) toforward the received content.

Media receiver 100 sends content 101 to transmitter device 140 via mediareceiver interface 102. In one embodiment, media receiver interface 102includes logic that converts content 101 into HDMI content. In such acase, media receiver interface 102 may comprise an HDMI plug and content101 is sent via a wired connection; however, the transfer could occurthrough a wireless connection. In another embodiment, content 101comprises DVI content.

In one embodiment, the transfer of content 101 between media receiverinterface 102 and transmitter device 140 occurs over a wired connection;however, the transfer could occur through a wireless connection.

Transmitter device 140 wirelessly transfers information to receiverdevice 141 using two wireless connections. One of the wirelessconnections is through a phased array antenna with adaptivebeam-forming. The other wireless connection is via wirelesscommunications channel 107, referred to herein as the back channel. Inone embodiment, wireless communications channel 107 is uni-directional.In an alternative embodiment, wireless communications channel 107 isbi-directional. In one embodiment, the back channel can use some or allof the same antennas as the forward beam-formed channel (part of 105).In another embodiment, the two sets of antennas are disjoint.

Receiver device 141 transfers the content received from transmitterdevice 140 to media player 114 via an interface such as a media playerinterface 113. In one embodiment, the transfer of the content betweenreceiver device 141 and media player interface 113 occurs through awired connection; however, the transfer could occur through a wirelessconnection. In one embodiment, media player interface 113 comprises anHDMI plug. Similarly, the transfer of the content between media playerinterface 113 and media player 114 occurs through a wired connection;however, the transfer could occur through a wireless connection. Thetransfer could also occur through a wired or wireless data interfacethat was not a media player interface.

Media player 114 causes the content to be played on display 115. In oneembodiment, the content is HDMI content and media player 114 transferthe media content to display via a wired connection; however, thetransfer could occur through a wireless connection. Display 115 maycomprise a plasma display, an LCD, a CRT, etc.

Note that the system in FIG. 1 may be altered to include a DVDplayer/recorder in place of a DVD player/recorder to receive, and playand/or record the content. The same techniques can be used in non-mediadata applications as well.

In one embodiment, transmitter 140 and media receiver interface 102 arepart of media receiver 100. Similarly, in one embodiment, receiver 141,media player interface 113, and media player 114 are all part of thesame device. In an alternative embodiment, receiver 140, media playerinterface 113, media player 114, and display 115 are all part of thedisplay. An example of such a device is shown in FIG. 2.

In one embodiment, transmitter device 140 comprises a processor 103, anoptional baseband processing component 104, a phased array antenna 105,and a wireless communication channel interface 106. Phased array antenna105 comprises a radio frequency (RF) transmitter having a digitallycontrolled phased array antenna coupled to and controlled by processor103 to transmit content to receiver device 141 using adaptivebeam-forming.

In one embodiment, receiver device 141 comprises a processor 112, anoptional baseband processing component 111, a phased array antenna 110,and a wireless communication channel interface 109. Phased array antenna110 comprises a radio frequency (RF) transmitter having a digitallycontrolled phased array antenna coupled to and controlled by processor112 to receive content from transmitter device 140 using adaptivebeam-forming.

In one embodiment, processor 103 generates baseband signals that areprocessed by baseband signal processing 104 prior to being wirelesslytransmitted by phased array antenna 105. In such a case, receiver device141 includes baseband signal processing to convert analog signalsreceived by phased array antenna 110 into baseband signals forprocessing by processor 112. In one embodiment, the baseband signals areorthogonal frequency division multiplex (OFDM) signals.

In one embodiment, transmitter device 140 and/or receiver device 141 arepart of separate transceivers.

Transmitter device 140 and receiver device 141 perform wirelesscommunication using a phased array antenna with adaptive beam-formingthat allows beam steering. Beam-forming is well known in the art. In oneembodiment, processor 103 sends digital control information to phasedarray antenna 105 to indicate an amount to shift one or more phaseshifters in phased array antenna 105 to steer a beam formed thereby in amanner well-known in the art. Processor 112 uses digital controlinformation as well to control phased array antenna 110. The digitalcontrol information is sent using control channel 121 in transmitterdevice 140 and control channel 122 in receiver device 141. In oneembodiment, the digital control information comprises a set ofcoefficients. In one embodiment, each of processors 103 and 112comprises a digital signal processor.

Wireless communication link interface 106 is coupled to processor 103and provides an interface between wireless communication link 107 andprocessor 103 to communicate antenna information relating to the use ofthe phased array antenna and to communicate information to facilitateplaying the content at the other location. In one embodiment, theinformation transferred between transmitter device 140 and receiverdevice 141 to facilitate playing the content includes encryption keyssent from processor 103 to processor 112 of receiver device 141 and oneor more acknowledgments from processor 112 of receiver device 141 toprocessor 103 of transmitter device 140.

Wireless communication link 107 also transfers antenna informationbetween transmitter device 140 and receiver device 141. Duringinitialization or tuning of the phased array antennas 105 and 110,wireless communication link 107 transfers information to enableprocessor 103 to select a direction for the phased array antenna 105. Inone embodiment, the information includes, but is not limited to, antennalocation information and performance information corresponding to theantenna location, such as one or more pairs of data that include theposition of phased array antenna 110 and the signal strength of thechannel for that antenna position. In another embodiment, theinformation includes, but is not limited to, information sent byprocessor 112 to processor 103 to enable processor 103 to determinewhich portions of phased array antenna 105 to use to transfer content.

When the phased array antennas 105 and 110 are operating in a modeduring which they may transfer content (e.g., HDMI content), wirelesscommunication link 107 transfers an indication of the status ofcommunication path from the processor 112 of receiver device 141. Theindication of the status of communication comprises an indication fromprocessor 112 that prompts processor 103 to steer the beam in anotherdirection (e.g., to another channel). Such prompting may occur inresponse to interference with transmission of portions of the content.The information may specify one or more alternative channels thatprocessor 103 may use.

In one embodiment, the antenna information comprises information sent byprocessor 112 to specify a location to which receiver device 141 is todirect phased array antenna 110. This may be useful duringinitialization when transmitter device 140 is telling receiver device141 where to position its antenna so that signal quality measurementscan be made to identify the best channels. The position specified may bean exact location or may be a relative location such as, for example,the next location in a predetermined location order being followed bytransmitter device 140 and receiver device 141.

In one embodiment, wireless communications link 107 transfersinformation from receiver device 141 to transmitter device 140specifying antenna characteristics of phased array antenna 110, or viceversa. In one embodiment, communications link 107 transfers informationfrom receiver device 141 to transmitter device 140 that can be used tocontrol phased array antenna 105.

An Example of a Transceiver Architecture

One embodiment of a transceiver is described below. The transceiverincludes transmit and receive paths for a transmitter and receiver,respectively. In one embodiment, the transmitter, for use incommunication with a receiver, comprises a processor and a phased arraybeamforming antenna. The processor controls the antenna to performadaptive beam steering using multiple transmit antennas in conjunctionwith receive antennas of the receiver by iteratively performing a set oftraining operations. One of the training operations comprises theprocessor causing the phased array beamforming antenna to transmit afirst training sequence while a receive antenna-array weight vector ofthe receiver is set and a transmitter antenna-array weight vectorswitches between weight vectors with a set of weight vectors. Another ofthe training operations comprises the processor causing the phased arraybeamforming antenna to transmit a second training sequence while atransmitter antenna-array weight vector is set as part of a process tocalculate the receive antenna-array weight vector.

In one embodiment, the receiver, for use in communication with atransmitter, comprises a processor and a phased array beamformingantenna. The processor controls the antenna to perform adaptive beamsteering using multiple receive antennas in conjunction with transmitantennas of the transmitter by iteratively performing a set of trainingoperations. One of the training operations comprises the processorsetting a receive antenna-array weight vector during a process forestimating a transmit antenna-array weight vector by having thetransmitter transmit a first training sequence while the receiveantenna-array weight vector is set. Another of the training operationscomprises the processor calculate the receive antenna-array weightvector when the transmitter transmits a second training sequence whilethe transmitter antenna-array weight vector is set.

FIGS. 3A and 3B are block diagrams of one embodiment of a transmitterdevice and a receiver device, respectively, that are part of an adaptivebeam forming multiple antenna radio system containing of FIG. 1.Transceiver 300 includes multiple independent transmit and receivechains and performs phased array beam forming using a phased array thattakes an identical RF signal and shifts the phase for one or moreantenna elements in the array to achieve beam steering.

Referring to FIG. 3A, digital baseband processing module (e.g., DigitalSignal Processor (DSP)) 301 formats the content and generates real timebaseband signals. Digital baseband processing module 301 may providemodulation, FEC coding, packet assembly, interleaving and automatic gaincontrol.

Digital baseband processing module 301 then forwards the basebandsignals to be modulated and sent out on the RF portion of thetransmitter. In one embodiment, the content is modulated into OFDMsignals in a manner well known in the art.

Digital-to-analog converter (DAC) 302 receives the digital signalsoutput from digital baseband processing module 301 and converts them toanalog signals. In one embodiment, the signal outputs from DAC 302 arebetween 0-1.7 GHz. Analog front end 303 receives the analog signals andfilters it with an appropriate low-pass image-rejection filter andamplifies it accordingly. The IF module 304 receives the output ofanalog front end 303 and up-converts it to the IF frequency. In oneembodiment, the IF frequency is between 2-15 GHz.

RF mixer 305 receives signals output from IF amplifier 304 and combinesthem with a signal from a local oscillator (LO) (not shown) in a mannerwell-known in the art. The signals output from mixer 305 are at anintermediate frequency. In one embodiment, the intermediate frequency isbetween 2-15 GHz.

Multiplexer 306 is coupled to receive the output from mixer 305 tocontrol which phase shifters 307 _(1-N) receive the signals. In oneembodiment, phase shifters 307 _(1-N) are quantized phase shifters. Inan alternative embodiment, phase shifters 307 _(1-N) may be replaced byIF or RF amplifiers with controllable gain and phase. In one embodiment,digital baseband processing module 201 also controls, via controlchannel 360, the phase and magnitude of the currents in each of theantenna elements in phased array antenna to produce a desired beampattern in a manner well-known in the art. In other words, digitalbaseband processing module 201 controls the phase shifters 307 _(1-N) ofphased array antenna to produce the desired pattern.

Each of phase shifters 307 _(1-K) produce an output that is sent to oneof power amplifiers 308 _(1-N), which amplify the signal. The amplifiedsignals are sent to an antenna array that has multiple antenna elements309 _(1-N). In one embodiment, the signals transmitted from antennas 309_(1-N) are radio frequency signals between 56-64 GHz. Thus, multiplebeams are output from the phased array antenna.

With respect to the receiver, antennas 310 _(1-N) receive the wirelesstransmissions from antennas 309 _(1-NK) and provide them to phaseshifters 312 _(1-N), via low-noise amplifiers 311 _(1-N), respectively.As discussed above, in one embodiment, phase shifters 312 _(1-N)comprise quantitized phase shifters. Alternatively, phase shifters 312_(1-N) may be replaced by complex multipliers. Phase shifters 312 _(1-N)receive the signals from antennas 310 _(1-N), which are combined by RFcombiner 313 to form a single line feed output. In one embodiment, amultiplexer is used to combine the signals from the different elementsand output the single feed line. The output of RF combiner 313 is inputto RF mixer 314.

Mixer 314 receives the output of the RF combiner 313 and combines itwith a signal from a LO (not shown) in a manner well-known in the art.In one embodiment, the output of mixer 314 is a signal with the IFcarrier frequency of 2-15 GHz. The IF module then down-converts the IFsignal to the baseband frequency. In one embodiment, there are I and Qsignals, which are between 0-1.7 GHz.

Analog-to-digital converter (ADC) 316 receives the output of IF 315 andconverts it to digital form. The digital output from ADC 316 is receivedby digital baseband processing module (e.g., DSP) 318. Digital basebandprocessing module 318 restores the amplitude and phase of the signal.Digital baseband processing module 318 may provide demodulation, packetdisassembly, de-interleaving and automatic gain.

In one embodiment, each of the transceivers includes a controllingmicroprocessor that sets up control information for the digital basebandprocessing module (e.g., DSP). The controlling microprocessor may be onthe same die as the digital baseband processing module (e.g., DSP).

DSP-Controlled Adaptive Beam Forming

In one embodiment, the DSPs implement an adaptive algorithm with thebeam forming weights being implemented in hardware. That is, thetransmitter and receiver work together to perform the beam forming in RFfrequency using digitally controlled analog phase shifters; however, inan alternative embodiment, the beam-forming is performed in IF. Phaseshifters 307 _(1-N) and 312 _(1-N) are controlled via control channel360 and control channel 370, respectfully, via their respective DSPs ina manner well known in the art. For example, digital baseband processingmodule (e.g., DSP) 301 controls phase shifters 307 _(1-N) to have thetransmitter perform adaptive beam-forming to steer the beam whiledigital baseband processing module (e.g., DSP) 318 controls phaseshifters 312 _(1-N) to direct antenna elements to receive the wirelesstransmission from antenna elements and combine the signals fromdifferent elements to form a single line feed output. In one embodiment,a multiplexer is used to combine the signals from the different elementsand output the single feed line. Note that processors (e.g., DSPs) thatcontrol the digital baseband processing modules, such as shown in thetransmitters and receivers of FIG. 1, could be coupled to controlchannels 360 and 370, respectively, could be used to control phaseshifters 307 _(1-N) and 312 _(1-N).

Digital baseband processing module (e.g., DSP) 301 performs the beamsteering by pulsing, or energizing, the appropriate phase shifterconnected to each antenna element. The pulsing algorithm under digitalbaseband processing module (e.g., DSP) 301 controls the phase and gainof each element. Performing DSP controlled phase array beam-forming iswell known in the art.

The adaptive beam forming antenna is used to avoid interferingobstructions. By adapting the beam forming and steering the beam, thecommunication can occur avoiding obstructions which may prevent orinterfere with the wireless transmissions between the transmitter andthe receiver.

In one embodiment, with respect to the adaptive beam-forming antennas,they have three phases of operations. The three phases of operations arethe training phase, a searching phase, and a tracking phase. Thetraining phase and searching phase occur during initialization. Thetraining phase determines the channel profile with predeterminedsequences of spatial patterns {A_(î)} and {B_(ĵ)}. The searching phasecomputes a list of candidate spatial patterns {A_(ī)}, {B _(j) } andselects a prime candidate {A ₀ , B ₀ } for use in the data transmissionbetween the transmitter of one transceiver and the receiver of another.The tracking phase keeps track of the strength of the candidate list.When the prime candidate is obstructed, the next pair of spatialpatterns is selected for use.

In one embodiment, during the training phase, the transmitter sends outa sequence of spatial patterns {A_(î)}. For each spatial pattern{A_(î)}, the receiver projects the received signal onto another sequenceof patterns {B_(ĵ)}. As a result of the projection, a channel profile isobtained over the pair {A_(î)}, {B_(ĵ)}.

In one embodiment, an exhaustive training is performed between thetransmitter and the receiver in which the antenna of the receiver ispositioned at all locations and the transmitter sending multiple spatialpatterns. Exhaustive training is well-known in the art. In this case, Mtransmit spatial patterns are transmitted by the transmitter and Nreceived spatial patterns are received by the receiver to form an N by Mchannel matrix. Thus, the transmitter goes through a pattern of transmitsectors and the receiver searches to find the strongest signal for thattransmission. Then the transmitter moves to the next sector. At the endof the exhaustive search process, a ranking of all the positions of thetransmitter and the receiver and the signals strengths of the channel atthose positions has been obtained. The information is maintained aspairs of positions of where the antennas are pointed and signalstrengths of the channels. The list may be used to steer the antennabeam in case of interference.

In an alternative embodiment, subspace training is used in which thespace is divided in successively narrow sections with orthogonal antennapatterns being sent to obtain a channel profile.

Assuming digital baseband processing module 301 (DSP) is in a stablestate and the direction the antenna should point is already determined.In the nominal state, the DSP will have a set of coefficients that itsends to the phase shifters. The coefficients indicate the amount ofphase the phase shifter is to shift the signal for its correspondingantennas. For example, digital baseband processing module 301 (DSP)sends a set digital control information to the phase shifters thatindicate the different phase shifters are to shift different amounts,e.g., shift 30 degrees, shift 45 degrees, shift 90 degrees, shift 180degrees, etc. Thus, the signal that goes to that antenna element will beshifted by a certain number of degrees of phase. The end result ofshifting, for example, 16, 32, 36, 64 elements in the array by differentamounts enables the antenna to be steered in a direction that providesthe most sensitive reception location for the receiving antenna. Thatis, the composite set of shifts over the entire antenna array providesthe ability to stir where the most sensitive point of the antenna ispointing over the hemisphere.

Note that in one embodiment the appropriate connection between thetransmitter and the receiver may not be a direct path from thetransmitter to the receiver. For example, the most appropriate path maybe to bounce off the ceiling.

The Back Channel

In one embodiment, the wireless communication system includes a backchannel 320, or link, for transmitting information between wirelesscommunication devices (e.g., a transmitter and receiver, a pair oftransceivers, etc.). The information is related to the beam-formingantennas and enables one or both of the wireless communication devicesto adapt the array of antenna elements to better direct the antennaelements of a transmitter to the antenna elements of the receivingdevice together. The information also includes information to facilitatethe use of the content being wirelessly transferred between the antennaelements of the transmitter and the receiver.

In FIGS. 3A and 3B, back channel 320 is coupled between digital basebandprocessing module (DSP) 318 and digital baseband processing module (DSP)301 to enable digital baseband processing module (DSP) 318 to sendtracking and control information to digital baseband processing module(DSP) 301. In one embodiment, back channel 320 functions as a high speeddownlink and an acknowledgement channel.

In one embodiment, the back channel is also used to transfer informationcorresponding to the application for which the wireless communication isoccurring (e.g., wireless video). Such information includes contentprotection information. For example, in one embodiment, the back channelis used to transfer encryption information (e.g., encryption keys andacknowledgements of encryption keys) when the transceivers aretransferring HDMI data. In such a case, the back channel is used forcontent protection communications.

More specifically, in HDMI, encryption is used to validate that the datasink is a permitted device (e.g., a permitted display). There is acontinuous stream of new encryption keys that is transferred whiletransferring the HDMI datastream to validate that the permitted devicehasn't changed. Blocks of frames for the HD TV data are encrypted withdifferent keys and then those keys have to be acknowledged back on backchannel 320 in order to validate the player. Back channel 220 transfersthe encryption keys in the forward direction to the receiver andacknowledgements of key receipts from the receiver in the returndirection. Thus, encrypted information is sent in both directions.

The use of the back channel for content protection communications isbeneficial because it avoids having to complete a lengthy retrainingprocess when such communications are sent along with content. Forexample, if a key from a transmitter is sent alongside the contentflowing across the primary link and that primary link breaks, it willforce a lengthy retrain of 2-3 seconds for a typical HDMI/HDCP system.In one embodiment, this separate bi-directional link that has higherreliability than the primary directional link given its omni-directionalorientation. By using this back channel for communication of the HDCPkeys and the appropriate acknowledgement back from the receiving device,the time consuming retraining can be avoided even in the event of themost impactful obstruction.

In the active mode, when the beam-forming antennas are transferringcontent, the back channel is used to allow the receiver to notify thetransmitter about the status of the channel. For example, while thechannel between the beam-forming antennas is of sufficient quality, thereceiver sends information over the back channel to indicate that thechannel is acceptable. The back channel may also be used by the receiverto send the transmitter quantifiable information indicating the qualityof the channel being used. If some form of interference (e.g., anobstruction) occurs that degrades the quality of the channel below anacceptable level or prevents transmissions completely between thebeam-forming antennas, the receiver can indicate that the channel is nolonger acceptable and/or can request a change in the channel over theback channel. The receiver may request a change to the next channel in apredetermined set of channels or may specify a specific channel for thetransmitter to use.

In one embodiment, the back channel is bi-directional. In such a case,in one embodiment, the transmitter uses the back channel to sendinformation to the receiver. Such information may include informationthat instructs the receiver to position its antenna elements atdifferent fixed locations that the transmitter would scan duringinitialization. The transmitter may specify this by specificallydesignating the location or by indicating that the receiver shouldproceed to the next location designated in a predetermined order or listthrough which both the transmitter and receiver are proceeding.

In one embodiment, the back channel is used by either or both of thetransmitter and the receiver to notify the other of specific antennacharacterization information. For example, the antenna characterizationinformation may specify that the antenna is capable of a resolution downto 6 degrees of radius and that the antenna has a certain number ofelements (e.g., 32 elements, 64 elements, etc.).

In one embodiment, communication on the back channel is performedwirelessly by using interface units. Any form of wireless communicationmay be used. In one embodiment, OFDM is used to transfer informationover the back channel. In another embodiment, CPM is used to transferinformation over the back channel.

Beam-forming Overview

In one embodiment, the communication system implements beam-forming withthe following elements: a beam-search process; a beam-tracking process;and a beam-steering state machine. The beam search and beam tracking areused to compensate for the time-variation of the wireless channel andthe possible obstruction of narrow beams. When called, the beam-searchprocess finds the beam direction that maximizes the link budget. Theobtained beam direction is then used for beam-forming. After thebeam-search process has resulted in optimal beam-forming, thebeam-tracking process tracks the beam versus small time-variations inthe channel transfer function. The beam-steering state machine uses anarbitrary bad link detection mechanism (which can based on payload orbeam-tracking results) to detect whether the Signal-to-Noise Ratio ofthe current link is below a desired threshold. For purposes herein, abad link means that current beam direction is obstructed, andsubsequently a new beam-search is scheduled to find the next best beamdirection.

FIG. 4 illustrates one embodiment of a beam-steering state machine.Referring to FIG. 4, state machine 400 includes an acquisition(initial/idle) state 401, a beam search state 402, and a steady-state,or data transfer state, 403. The beam steering process begins inacquisition state 401. In one embodiment, acquisition state 401 is onlyentered once during link setup. After initial acquisition, state machine400 transitions to beam search state 402 to perform the beam search.Beam search state 402 is also entered as soon as a source (e.g., atransmitter) or destination (e.g., a receiver) determines that a channelis considered bad (e.g., beam obstructed) (based on one or moremetrics). Note that in one embodiment, the beam search is scheduledregularly (e.g., every 0.5-2 sec) during data transfer state 403. Thismay be useful in based of the beam being blocked.

After the beam search is successful, state machine 400 transitions intosteady-state 403 where data transfer operations are performed. In oneembodiment, this includes beam tracking at predetermined intervals(e.g., every 1-2 msec). In one embodiment, the beam tracking is ashortened version of the beam search process. These may be scheduled orbased on request.

If there is a link failure that occurs when beam steering state machine400 is in either beam search state 402 or data transfer state 403, thenbeam steering state machine 400 transitions to acquisition state 401.

In one embodiment, beam-forming at the transmitter is performed byrotating the phase of the RF-modulated signal individually for each RFpower amplifier and transmit antenna set, where phase rotation isdescribed by the following equation:

and the rotation angle θ is quantized to 2-4 bits. This may be achievedusing quantized phase shifters.

Similarly, in one embodiment, beam-forming at the receiver is performedby rotating the phase of the received RF-modulated signal after eachreceive antenna and Low-Noise Amplifier (LNA) set, and then combiningthe phase-rotated signals.

It should be noted that in one embodiment, the receive antennas arecoupled to one or more digitization paths, and the number ofdigitization paths is less than the number of receive antennas. Also, inone embodiment, the transmit antennas are coupled to one or moretransmit signal generation paths, and the number of transmit signalgeneration paths are less than the number of transmit antennas.

An Example of a Beam-Search Process

In one embodiment, the beam-search process consists of two stages:timing recovery and an iterative beam-search. In the timing recoverystage, arrival time (delay) of the beam/ray with maximum gain isestimated. In one embodiment, delay estimation is performed bytransmitting a known symbol sequence over the air and matching thatsequence at the receiver via a matched filter. To maximize thesignal-to-noise ratio, transmit antenna phases are set equal to columnsof the N×N Hadamard matrix, H, one column at a time, where H has thefollowing properties:H(i,j)∈{−1,1}, H ^(T) H=NI _(N×N)where H^(T) is transpose of H, and I_(N×N) is the N×N identity matrix.Transmit antenna phases are swept through N columns of H (set equal toone at a time) P (e.g., 3) times, where each time a different receiveantenna phase pattern is used. Receive antenna phase patterns areselected such that the corresponding beams cover the entire space. Thereceiver matched filter correlates the received signal, r(k), with thetransmitted sequence, x(k), as described by the following equation,where the pattern is L symbol long:

${y(k)} = {\sum\limits_{i = 0}^{L - 1}{{r\left( {k + i} \right)}{x(i)}}}$

The time delay that results in a maximum matched-filter output energy,after it is summed over all transmit and receive antenna phase patterns,is selected as the time-delay of the maximum gain beam/ray. In addition,the receive antenna phase pattern, for which the matched-filter outputat the selected time-delay has maximum energy, after it is summed overall transmit antenna phase patterns, is also selected.

At the next stage, a beam-search iterative process is used that, in oneembodiment, alternatively changes transmit and receive phase patternsfor a total of 2M (even) number (e.g., 4, 6, 8 or 10) of stages. Inalmost all cases, transmit and receive phase patterns converge towardsthe optimum values corresponding to the maximum-gain beam direction. Insome isolated cases, the transmit and receive phase patterns mayfluctuate between different phase patterns that correspond to similarbeam-forming gains.

For the first iteration, the receive phase pattern is set to one of theP phase patterns that was selected at the end of the lasttiming-recovery stage. In other words, the receiver phase shifts are setto an ith initial value (for i=1, 2, 3, etc.). In one embodiment, thereceive phase shifts are set by setting values of an antenna-arrayweight vector (AWV). The transmit pattern, on the other hand, is setequal to N columns of the Hadamard Matrix H one at a time. An example ofa 36×36 Hadamard matrix is given in FIG. 8. Note that for a certainnumber of antennas, another unitary matrix could be used. Also, notethat in one embodiment, the antenna-array weight vectors (AWV) for thereceiver and the transmitter are complex weight vectors that can havemagnitude and/or phase information. In one embodiment, the weightvectors are quantized phase shift vectors.

The transmitter transmits known symbol sequence over the air, which isused to estimate resulting Single-Input Single-Output (SISO) channeltransfer functions from the RF-modulated signal before N transmitantenna phase rotations to the combined signal after N receive antennaphase rotations. During this stage, the transmitter phased array antennaswitches between phase vectors derived from columns of matrix H, whichspan the entire space. In one embodiment, the transmitter antenna arrayweight vector (AWV) includes 36 weight vectors. For each transmit phasepattern, the received signal is correlated with the transmitted symbolsequence at the selected optimum time-delay. The complex-valuedcorrelator output, ĥ=Ae^(jφ), is then used as the estimate of thecorresponding channel transfer function. Thus, the N-Tx by 1-Rx channelgains per each delay corresponding to the receiver phase shifts aresequentially measured and the maximum-energy delay (e.g., cluster) isselected for the best initial value.

Next, the vector of N complex-valued channel estimates iscomplex-conjugated and multiplied by matrix H. Angles of thecomplex-valued elements of this vector are then quantized into 2-4 bits,forming a vector of quantized phases. This vector is referred to hereinas the MRC-based transmitter quantized phase shift (QPS) vector (i.e.,the transmitter AWV) and is sent back to the transmitter via a reversewireless channel such as the back channel described above, where it isused as the fixed transmit phase pattern for the next part of the firstiteration. In one embodiment, the index of the transmitter AWV thatproduces the strongest signal at the receiver is also sent back to thetransmitter via the reverse channel.

For the next part of the first iteration, the transmit phase pattern isset equal to the quantized phase vector calculated at the end of lastiteration. That is, the transmitter phase shifts are set to the valuescalculated in the first part of the iteration that is for tuning of thetransmitter AWV. The receive phase pattern, on the other hand, is setequal to the N columns of H one at a time. Transmitting the same symbolsequence and using the same correlation procedure, SISO channel transferfunctions are estimated for each receive phase pattern. In other words,the 1-Tx by N-Rx channel gains are sequentially measured at the receiverfor maximum-energy delay and an estimate for the equivalent 1×M channel.

Similarly, the vector of N complex-valued channel estimates iscomplex-conjugated and multiplied by H. Angles of the complex-valuedelements of this vector are then quantized into 2-4 bits, forming avector of quantized phases. This vector is referred to as the MRC-basedreceiver quantized phase shift (QPS) vector (i.e., the receiver AWV).This AWV vector is used in the receiver as the fixed receive phasepattern for the next iteration. That is, the receiver phase shifts(weights) are set to these calculated values.

Thus, the same steps are repeated a number of times (e.g., 3, 4, etc.),where alternatively transmit or receive phase patterns are set equal tocalculated quantized phase vectors from the previous iteration, whilethe patterns for the opposite operation, i.e., receive or transmitpatterns, are set equal to N columns of H one at a time.

At the end of the iterations, the calculated transmit and receive phasevectors are used to form a beam in the optimum direction.

In one embodiment, the beam search (and beam tracking) signal is anOQPSK signal at F_(s)/2 sampling frequency, where F_(s) is the OFDMsampling rate.

In one embodiment, up to three different initial receiver QPS vectorsare used to improve performance of the optimum sampling-time estimation.Also, in one embodiment, the sequential channel estimation is performedby setting the transmitter (and receiver) weight vector to N columns ofmatrix H, one at time, and measuring N corresponding scalar channelestimates sequentially. Each channel estimation stage consists of Nestimation intervals such that if V is the resulting 1×N (N×1) estimatevector, then the channel estimate is VH* (H*V)

The received signal should be neither saturated nor over-attenuatedduring each timing-recovery or iteration step, where transmit or receivephase patterns are swept through columns of H. Hence, an Automatic GainControl (AGC) procedure is performed before each such step. In oneembodiment, in this AGC procedure, an arbitrary symbol sequence coveringthe same bandwidth is transmitted over the air, while transmit andreceive phase patterns are changed in the same fashion as the ensuingstep. The received signal energy is measured, and the receiver gain isconsequently set to a value such that the received signal is neithersaturated nor over-attenuated for all transmit and receive phasepatterns. If necessary, this procedure will be repeated a number oftimes (up to 3) until a suitable gain is found.

FIG. 5 illustrates stages of one embodiment of the beam search processdescribed above. Referring to FIG. 5, stages 501-503 represent timingrecovery stages. During these stages, the initial receiver phase shiftvectors and the optimum delay are selected. In one embodiment, duringstages 501 and 502, the transmit energy is fixed.

After stage 503, a series of iterations is performed. Each iterationconsists of three blocks, with stages 504-506 representing an example ofone iteration. Stage 504 is a transmit channel estimate stage using afixed receive phase pattern in which the receiver vectors that give thebest energy are selected and used to estimate the channel. As shown,stage 504 includes automatic gain control 504 ₁ along with a block inwhich the receiver generates a N×1 channel estimate using receivedvectors and calculates the transmit phase shift vector in substage 504₂. The operations of substage 504 ₂ are depicted in block form shown asan expanded version of substage 520 ₂ (since all the block are thesame). Initially, the transmit phase shift vector is changed to H1(substage 550 ₁), with a guard interval (substage 550 ₂) inserted tocompensate for the phase shift latency. For a change in the transmitweight vectors, the guard interval is larger than the overall delayspread minus the transmit filter delay spread. Then the first channel(Ch1) is measured (block 550 ₃). After measuring the channel, thetransmit phase shift vector is changed to H2 (substage 550 ₄), with aguard interval (substage 550 ₅). Then the second channel (Ch2) ismeasured (substage 550 ₆). This continues until the last channel, ChN,is measured. After all the transmit phase shift vectors have beentransmitted and the channels estimated, the transmit phase shift vectorsare calculated and changed (in preparation for estimating the receiverchannel). In one embodiment, the transmitter antenna weight vector thatproduces the strongest received signal at the receiver is repeated morethan once during this stage in order to allow the receiver to compensatefor various phase inaccuracies inherent to the transmitter and receiveranalog circuits.

After the transmit phase shift vector has been calculated, the receiversends it back to the transmitter in stage 505. In one embodiment, thereceiver additionally sends back the index of the transmitter weightvector that produces the strongest received signal to be used during thenext iterations. This may be performed using the backchannel.

Next, the receive channel estimation stage 506 is performed using thefixed transmit phase shift vector. The receive channel estimation stage(stage 506), as well as each of the other receive channel estimationstages, comprises an automatic gain control substage (substage 506 ₁)and a 1×N channel estimation and receive phase shift vector calculationstage (substage 506 ₂). AGC block 506 ₁ is depicted as three AGC blocks531, numbers 1-3, which are all the same. One of these is shown in moredetail and is exemplary of the others. First, the receive phase shiftvector is changed to H1 (substage 531 ₁) and AGC is performed on thatphase shift vector (block 531 ₂). Then the receive phase shift vector ischanged to H2 (substage 531 ₃) and AGC is performed on that phase shiftvector (substage 531 ₄). This continues for all N receive phase shiftvectors.

After AGC substage 506 ₁, the channel estimate and receive phase shiftvector calculation occurs at substage 506 ₂. The operations of substage506 ₂ are depicted in block form and are the same for all such blocks inFIG. 5. Initially, the receive phase shift vector is changed to H1(substage 560 ₁), with a guard interval (substage 560 ₂) inserted tocompensate for the phase shift latency. For a change in the receiveweight vectors, the guard interval is larger than the overall delayspread minus the receive filter delay spread. Then the first channel(Ch1) is measured (substage 560 ₃). After measuring the channel, thereceive phase shift vector is changed to H2 (substage 560 ₄), with aguard interval (substage 560 ₅). Then the second channel (Ch2) ismeasured (substage 560 ₆). This continues until the last channel, ChN,is measured. After all the receive phase shift vectors have beentransmitted and the channels estimated, the receive phase shift vectorsare calculated and changed. In one embodiment, with four iterations,there are fourteen stages.

Automatic Gain Control

The signal sent during AGC tuning intervals uses the same modulation butcarries no information.

The AGC gain should be constant during each channel estimation stage.During each stage, either the transmit or receive weight vectors arechanged (sweeping through N columns), which results in RSSI fluctuation.In this case, the AGC is run for all N possible weight vectors, the AGClevel is fixed to the minimum obtained value, and then N channelestimations are performed.

FIG. 6 illustrates a particular beam-forming that resulted from the beamsearch process of FIG. 5.

FIG. 7 illustrates one embodiment of a beam search and tracking diagramat the source/transmitter. Referring to FIG. 7, a BPSK beam searchpattern 701 is at a frequency of F_(s)/2 is filtered using oversamplingcoal shaping filter 702, or produces the beam search pattern to afrequency f_(s). This pattern is then sent to OQPSK mapping 703, whichmaps the BPSK symbols −1 and 1 to complex QPSK symbols −1−j and 1+jrespectively, and delays the Q component by half a sample with respectto the I component. The output of OQPSK mapping 703 is converted toanalog using DAC 704 and is then filtered using analog filter 705 priorto transmission.

An Example of a Beam-Tracking Algorithm

In one embodiment, the beam-tracking algorithm consists of twoiterations of the iterative beam-search process, e.g. the 2^(nd) and3^(rd) iterations, described above. FIG. 9 is a flow diagram of oneembodiment of the beam-tracking process. Referring to FIG. 9, in thefirst iteration (shown as block 901), the transmit phase pattern is setequal to the transmit phase vector corresponding to the current beam(i.e., the transmit phase shifts are set to the current estimates),while the receive phase pattern is swept through N columns of H for thecurrent delay. From this operation, the MRC-based receive quantizedphase shift vector is calculated. The calculated quantized phase vectoris then used as the fixed receive phase pattern for the second iteration(shown as block 902), while the transmit phase pattern is swept throughN columns of H and the MRC-based transmit quantized phase shift vectorsare calculated. In one embodiment, the transmitter phase pattern thatproduces the strongest received signal at the receiver is repeated morethan once during this stage in order to allow the receiver to compensatefor various phase inaccuracies inherent to the transmitter and receiveranalog circuits. In each iteration, channel transfer functions areestimated for the same time-delay that was derived in thetiming-recovery stage of the beam-search process. The transmitterquantized phase vectors calculated in these iterations are then fed back(903) to be used as the transmit phase patterns. In one embodiment, theindex of the weight vector that produces the strongest received signalis additionally fed back to be used during the next beam-trackinginstance. Note that blocks 901 and 902 are described in more detail inthe same manner as FIG. 5 above.

The same AGC procedure as described above in the beam-search process isperformed before each iteration in order to ensure that the receivedsignal is neither saturated nor over-attenuated during the ensuingoperation. These are shown in FIG. 9, with example AGC tuning for onechannel, which is the same as the others, being shown in detail.

Alternative Embodiments of a Beam-Search Algorithm

A second, alternative embodiment of a beam-search process is shown inFIG. 10. Referring to FIG. 10, first, a known symbol sequence istransmitted over the air, which is used to estimate the channel. Next,the transmit phase pattern is set equal to N columns of H one at a time.For each such transmit phase pattern, the receive phase pattern is thenset equal to N columns of H one at a time, resulting in N×N differenttransmit and receive phase pattern combination.

Afterwards, the N×N corresponding SISO channel transfer functions areestimated by matching the received signal with the given symbol sequenceat the optimum time-delay (the timing-recovery procedure is similar tothe first embodiment of the beam-search process except that allcombinations of transmit and receive antenna patterns shall be used).The N×N estimates are used to form an N×N matrix, Γ. Γ is thenmultiplied by H and transpose of H as in the following equation:G=HΓH^(T)where G is the MIMO channel transfer function estimate.

The following iteration is then performed for k=1, . . . , M:z=conj(G ^(T) u _(k−1)), v_(k)=quant([

z₁,

z₂, . . . ,

z_(N)]) w=conj(Gv _(k−1)), u_(k)=([

w₁,

w₂, . . . ,

w_(N)])where u₀ is the arbitrary initial receive phase pattern.

The above estimation phase is preceded by an AGC procedure similar tothe AGC procedure described above. This AGC procedure, which measuresthe received signal energy for all transmit and phase patterncombinations, and can be repeated a few times as needed, ensures thatthe received signal is neither saturated nor over-attenuated during theestimation.

Applications

In one embodiment, the above beam-forming schemes are applied to asystem operating in the 57 to 64 GHZ unlicensed band. Compared to otherlower frequency unlicensed bands such as 2.4 GHz and 5 GHz, the 60 GHzband allows usage of much smaller antennas with similar antenna gains.Ideally, 60 GHz antennas can be 12 times smaller than 5 GHz antennaswith same gain. This means that a much larger number of antennas can beused without substantially increasing the wireless system dimensions,and hence cost.

In addition, measurements show that the 60 GHz band propagation channelis more clustered than the 2.4 and 5 GHz bands. This is equivalent tosaying that for this band the propagation paths can be grouped intodistinct clusters. FIG. 11 demonstrates the notion of a clusteredpropagation channel. The beam-forming process described above is thenideally equivalent to focusing propagation within the cluster withmaximum gain. It can be shown for such clustered channels, channelcapacity under the beam-forming scheme described herein is often veryclose to the maximum MIMO channel capacity (achievable via multiplexingas mentioned in the Background Section). In addition, focusingpropagation within a cluster means that the propagation delay spreadwill be equal to the cluster delay-spread which can be significantlylower than overall channel delay-spread.

Therefore, the proposed beam-forming method is very suitable forwireless applications in the 60 GHz band.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that anyparticular embodiment shown and described by way of illustration is inno way intended to be considered limiting. Therefore, references todetails of various embodiments are not intended to limit the scope ofthe claims which in themselves recite only those features regarded asessential to the invention.

1. A method comprising: performing adaptive beam steering using multipletransmit and receive antennas, including iteratively performing a pairof training sequences, wherein the pair of training sequences includesestimating a transmitter antenna-array weight vector and a receiverantenna-array weight vector, wherein performing adaptive beam steeringusing multiple transmit and receive antennas comprises iterativelyperforming a set of operations, the set of operations including (a)setting a receive weight vector for receive antennas based on an initialweight vector or phase shift vector; (b) sequentially measuring channelgains corresponding to each phase to form a first set of channel gains;(c) calculating a second weight vector based on the first set of channelgains; (d) setting transmit phase shifts for transmit antennas based onthe second weight vector; (e) sequentially measuring channel gains atthe receiver corresponding to each phase to form a second set of channelgains; and (f) calculating a third weight vector based on the second setof measured channel gains.
 2. The method defined in claim 1 whereiniteratively performing the set of operations is performed such that theset of operations is performed four times.
 3. A method comprising:performing adaptive beam steering using multiple transmit and receiveantennas, including iteratively performing a pair of training sequences,wherein the pair of training sequences includes estimating a transmitterantenna-array weight vector and a receiver antenna-array weight vector,further comprising: estimating a first channel from a first set ofchannel gains, wherein calculating a first phase shift vector is basedon the estimate of the first channel, wherein estimating the firstchannel comprises using a unitary matrix as a transfer matrix, such thattransmit antenna weight vector is set to a column of the unitary matrixone column at a time; and estimating a second channel from a second setof channel gains, wherein calculating a second phase shift vector isbased on the estimate of the second channel.
 4. A method comprising:performing adaptive beam steering using multiple transmit and receiveantennas, including iteratively performing a pair of training sequences,wherein the pair of training sequences includes estimating a transmitterantenna-array weight vector and a receiver antenna-array weight vector,further comprising: estimating a first channel from the first set ofchannel gains, wherein calculating the second phase shift vector isbased on the estimate of the first channel, wherein estimating the firstchannel comprises using a Hadamard-type matrix as a transfer matrix,such that transmit antenna weight vector is set to a column of theHadamard-type matrix one column at a time; and estimating a secondchannel from the second set of channel gains, wherein calculating thethird phase shift vector is based on the estimate of the second channel.5. A method comprising: performing adaptive beam steering using multipletransmit and receive antennas, including iteratively performing a pairof training sequences, wherein the pair of training sequences includesestimating a transmitter antenna-array weight vector and a receiverantenna-array weight vector, further comprising: estimating a firstchannel from a first set of channel gains, wherein calculating a firstphase shift vector is based on the estimate of the first channel,wherein estimating the first channel comprises estimating channel vectorelements one at a time; and estimating a second channel from a secondset of channel gains, wherein calculating a second phase shift vector isbased on the estimate of the second channel.
 6. The method defined inclaim 5 wherein a number of sequential estimation slots is set to anumber, and further wherein the number is
 36. 7. The method defined inclaim 5 wherein a number of sequential estimation slots is set to anumber, and further wherein the number of sequential estimations isgreater than the number of different transmit antenna weight vectors,and the transmitter antenna weight vector that produces the strongestreceived signal at the receiver is repeated more than once.
 8. Themethod defined in claim 5 wherein a number of sequential estimationslots is set to a number, and further wherein the number of sequentialestimations is 36, and the transmitter antenna weight vector thatproduces the strongest received signal at the receiver is repeated 10times.
 9. An apparatus comprising: a transceiver having a first digitalbaseband processing unit coupled to a first phased array antenna; and areceiver having a second digital baseband processing unit coupled to asecond phased array antenna, wherein the first and second digitalbaseband processing units cooperate to perform adaptive beam steering,using multiple transmit and receive antennas, by iteratively performinga pair of trainings, wherein the pair of trainings includes estimating atransmitter antenna-array weight vector and a receiver antenna-arrayweight vector, and wherein said iteratively performing the pair oftraining sequences includes alternatively changing transmit and receivephase patterns for a plurality of iterations; wherein the first andsecond digital baseband processing units cooperate to perform adaptivebeam steering by using a set of operations performed iteratively, theset of operations including: (a) the second digital baseband processingunit setting receive phase shifts for receive antennas of the secondphased array antenna based on a first weight vector; (b) the seconddigital baseband processing unit causing channel gains corresponding toeach phase to be sequentially measured and forming a first set ofchannel gains; (c) the second digital baseband processing unitcalculating a second weight vector based on the first set of channelgains; (d) the first digital baseband processing unit setting transmitphase shifts for transmit antennas of the first phased array antennabased on the second weight vector; (e) the second digital basebandprocessing unit causing channel gains corresponding to each phase to bemeasured at the receiver and forming a second set of channel gains; and(f) the second digital baseband processing unit calculating a thirdweight vector based on the second set of measured channel gains, whereinthe second digital baseband processing unit estimates the first channelby using a unitary matrix as a transfer matrix, such that transmitantenna weight vector is set to columns of the unitary matrix.
 10. Anapparatus comprising: a transceiver having a first digital basebandprocessing unit coupled to a first phased array antenna; and a receiverhaving a second digital baseband processing unit coupled to a secondphased array antenna, wherein the first and second digital basebandprocessing units cooperate to perform adaptive beam steering, usingmultiple transmit and receive antennas, by iteratively performing a pairof trainings, wherein the pair of trainings includes estimating atransmitter antenna-array weight vector and a receiver antenna-arrayweight vector, and wherein said iteratively performing the pair oftraining sequences includes alternatively changing transmit and receivephase patterns for a plurality of iterations; wherein the first andsecond digital baseband processing units cooperate to perform adaptivebeam steering by using a set of operations performed iteratively, theset of operations including (a) the second digital baseband processingunit setting receive phase shifts for receive antennas of the secondphased array antenna based on a first weight vector; (b) the seconddigital baseband processing unit causing channel gains corresponding toeach phase to be sequentially measured and forming a first set ofchannel gains; (c) the second digital baseband processing unitcalculating a second weight vector based on the first set of channelgains; (d) the first digital baseband processing unit setting transmitphase shifts for transmit antennas of the first phased array antennabased on the second weight vector; (e) the second digital basebandprocessing unit causing channel gains corresponding to each phase to bemeasured at the receiver and forming a second set of channel gains; and(f) the second digital baseband processing unit calculating a thirdweight vector based on the second set of measured channel gains, whereinthe second digital baseband processing unit estimates the first channelby using a Hadamard-type matrix as a transfer matrix, such that transmitantenna weight vector is set to columns of the Hadamard-type matrix.